Method and apparatus for grinding composite workpieces

ABSTRACT

A method is described for grinding a composite workpiece to form a component having concentric and eccentric cylindrical regions. The method comprises mounting the workpiece in a computer controlled grinding machine having a grinding wheel the advance and withdrawal of which is controllable by a program entered into the controlling computer, loading a wheelfeed controlling program into the computer, relatively positioning the grinding wheel and the workpiece to align the wheel with a first selected region of the workpiece, advancing the grinding wheel towards the selected region so as to grind the surface thereof, controlling the wheelfeed so as to maintain grinding contact between the grinding wheel and the workpiece so as either to grind a concentric cylindrical region thereon or an offset cylindrical region thereon as required, information about each selected region of the workpiece being stored in the computer and addressed as appropriate so that the wheelfeed can be controlled appropriately depending on whether a selected workpiece region is to be ground as a concentric or an offset cylindrical region. The method allows a workpiece having both concentric and offset cylindrical regions thereon to be ground using a single grinding machine under computer control without demounting the workpiece from the machine. A computer controlled grinding machine is described as are programs for controlling the machine.

FIELD OF INVENTION

This invention concerns methods and apparatus for grinding of workpiecesto form components which include both concentric and eccentriccylindrical regions. Such a component is an internal combustion enginecrankshaft which includes both concentric journal bearing regions andeccentric crankpins. The invention is applicable to any such workpiecewhich is to be ground to size and finish, and such workpieces will bereferred to herein as composite workpieces.

BACKGROUND TO THE INVENTION

Historically workpieces of this nature have been ground on two grindingmachines. A first grinding machine has been used to grind the concentriccylindrical sections and a second grinding machine has been used togrind the eccentric cylindrical sections.

In the first grinding machine the workpiece is rotated about its primaryaxis and each of the concentric sections are ground by moving a grindingwheel into a grinding position and removing material from the workpieceto produce a concentric cylindrical region thereon, in a conventionalmanner.

In the second grinding machine, two approaches have been adopted. In oneapproach the workpiece has been rotated about the axis of each eccentricregion in turn, and conventional cylindrical grinding is employed toremove material so as to produce a cylindrical bearing surface at eacheccentric region, just as if the element were a concentric cylindricalregion of an overall workpiece. In the second approach, the workpiecehas been rotated about its primary axis so that the eccentric regionsprecess eccentrically around the primary axis of rotation, as forexample do the crankpins of a crankshaft when the latter is mounted inand is rotated in an engine. In this second approach the grinding wheelhas been aligned with an eccentric region and then been advanced andretracted under computer control in synchronism with the precession ofthe eccentric region so that the grinding wheel remains in contacttherewith at all times. The region is thereby ground at all positions ofits precession. As each eccentric region is ground to size, the grindingwheel is withdrawn and the workpiece or grinding wheel is repositionedaxially so that another eccentric region is aligned with the grindingwheel, ready for a similar grinding operation at the new location.

A process requiring two grinding machines involves considerabledown-time as components are moved from one machine to another.

During any grinding operation, but particularly noticeable when grindingregions of an elongate workpiece (such as a crankshaft) which issupported for grinding at its ends, unwanted eccentricity may beintroduced into the workpiece due to forces acting on the workpieceduring the grinding process. This eccentricity which is termed runouttends to be more noticeable in concentrically ground cylindrical regionsof the workpiece. It often appears as a consequence of stress relievingthe workpiece, after grinding, and any eccentricity introduced intoconcentrically ground journal bearing regions a crankshaft willintroduce undesirable wear in the component when mounted and rotated inuse.

It is one object of the invention to reduce the machining time requiredto machine composite workpieces containing both concentric and eccentricregions, such as crankshafts which contain concentric Journal bearingregions and eccentric crankpins.

It is a subsidiary object of the invention to reduce unwantedeccentricity of concentrically ground cylindrical regions of a compositeworkpiece such as concentric cylindrical bearing regions.

It is a further object to provide a method and apparatus which will notonly reduce machining time of composite workpieces but also allowseccentricity correction to be applied to both concentrically andeccentrically ground cylindrical workpiece regions such as the joinedbearing regions and the workpiece of an engine crankshaft.

SUMMARY OF THE INVENTION

(a) Composite Workpiece Grinding in Accordance With the Invention

A method of grinding a composite workpiece to form a component havingconcentric and eccentric cylindrical regions, comprises, mounting theworkpiece in a computer controlled grinding machine having a grindingwheel the advance and withdrawal of which is controllable by a programentered ito the machine controlling computer, loading a wheelfeedcontrolling program into the computer, positioning the grinding wheelrelative to the workpiece, or the workpiece relative to the grindingwheel, so that the wheel is aligned with a first selected region of theworkpiece, advancing the grinding wheel towards the selected region soas to grind the surface thereof, controlling the wheel feed so as tomaintain grinding contact between the grinding wheel and the workpieceso as either to grind a concentric cylindrical region thereon or togrind an eccentric cylindrical region thereon as required, informationabout each selected region of the workpiece being stored in the computermemory which is addressed as appropriate so that the wheel feed can becontrolled appropriately depending on whether a selected workpieceregion is to be ground as a concentric or an eccentric cylindricalregion.

The invention allows a workpiece having both concentric and eccentriccylindrical regions thereon to be ground on a single grinding machinewithout demounting the workpiece from the machine. This enables aworkpiece to be left in place between centres whilst different regionstherealong are ground to form cylindrical surfaces some of which areconcentric with the primary axis of rotation of the workpiece, andothers of which are eccentric relative thereto.

The invention is of particular application to the grinding ofcrankshafts which have journal bearing regions which have to be groundas cylindrical surfaces concentric with the primary axis of rotation ofthe crankshaft and crankpins which have to be ground as cylindricalsurfaces eccentric to the primary axis of rotation.

(b) Correction For Process Induced Eccentricity

During the grinding of any workpiece, stresses and strains introduced bythe grinding process particularly in unsupported regions of theworkpiece, can cause a cylindrical region which is being ground tobecome eccentric relative to the primary workpiece axis. Whilst theseeccentricities may be of minor consequence in the case of asignificantly eccentric region such as a crankpin of a crankshaft, minoreccentricities in what should be concentric cylindrical surface such asa journal bearing surface of a crankshaft, will result in friction andwear in an engine in which such a crankshaft is mounted.

The invention allows for this problem to be overcome in that the controlsystem can be programmed so as to not only distinguish betweenconcentric and eccentric regions of a workpiece to enable the wheel feedto be controlled accordingly (so as to grind a cylindrical surfaceconcentric with the primary axis of the workpiece or a cylindricalsurface which is eccentric thereto), (ie whose axis is spaced from butparallel to the said primary axis) but is also capable of beingcontrolled so as to introduce small advance and retract movements in thewheel feed whilst the grinding wheel is engaged in grinding a concentriccylindrical workpiece region, so as to introduce into the ground regionan eccentricity in the cylindrical surface which is equal and oppositeto any eccentricity which the grinding process per se introduces intothe ground region, so that the two cancel out.

The invention also provides for the control system as aforesaid to beprogrammed to adjust the wheel feed program instructions or controlsignals when grinding eccentric cylindrical surfaces, so as to introducean additional eccentricity which is equal and opposite to any stressinduced eccentricity introduced into the eccentric cylindrical surfaceby the grinding process.

This technique of eccentricity compensation therefore may be extended toinclude not only the grinding of concentric cylindrical workpiecesurfaces but also the grinding of eccentric cylindrical workpiecesurfaces.

(c) Setting Up

A method of setting up such a grinding machine for grinding a compositeworkpiece with compensation for process induced eccentricity toconcentric cylindrical regions comprises the steps of cylindricallygrinding at least one concentric workpiece region to final form,measuring any unwanted eccentricity introduced by the grinding processtogether with the angular position(s) thereof in the said at least oneworkpiece region, and adjusting the wheel feed program, instructions orcontrol signals stored in the computer controlling the grinding machineso that during subsequent workpiece grinding, the wheel feed iscontrolled so as to grind an equal and opposite eccentric form to thatmeasured, thereby to cancel out process induced eccentricity.

Preferably the measuring of the workpiece region occurs after it hasbeen stress relieved, which may be achieved merely by disengaging thegrinding wheel, but may involve removing the workpiece from the grindingmachine for gauging, then the careful replacement of the workpiece backin position.

Any unwanted eccentricity introduced into a workpiece by a grindingprocess will tend to vary from one position to another along the lengthof the workpiece, and will tend to increase with distance from asupported workpiece end. In consequence for example cylindrical journalbearing regions and crankpins near the centre of a crankshaft which issupported at opposite ends may require a greater degree of eccentricitycompensation than is the case for those near to the two supported ends.

Where a plurality of such regions are to be ground at spaced apartpositions axially along a workpiece which is supported at opposite ends,the setting up process may be performed for a concentric cylindricalregion approximately midway along the said axial length of theworkpiece, and proportionately reduced corrections are applied to thewheelfeed program instructions or control signals for similarcylindrical regions which are to be ground and which are displaced fromthe mid position towards the supported ends of the workpiece.

In an alternative method, it is possible to more fully take into accountthe variation in unwanted eccentricity introduced by grinding processforces along the axial length an elongate workpiece supported atopposite ends, such that regions towards the centre of the workpiece,tend to require a greater degree of eccentricity compensation duringgrinding than do those adjacent the supported ends thereof. Thisalternative method involves the steps of concentrically grinding all ofthe concentric surfaces of a workpiece without introducing anycompensation for unwanted process induced eccentricity thereafter makingmeasurements on the workpiece to determine the extent and angularposition of an unwanted eccentricity for each of the ground regions, andseparately adjusting the wheelfeed program instructions or controlsignals used to control the wheel feed during subsequent grinding ofeach said region of the same of a similar workpiece, so as to compensateindividually for each said region for any process-induced eccentricity.

After such a setting up process has been performed and the originalworkpiece has been reground using the corrected wheelfeed programinstructions or control signals a further check on the regroundworkpiece may be made and second order corrections may be made to theinstructions or control signals, before regrinding the originalworkpiece or grinding further similar workpieces.

Measurements may be made subsequent to each further workpiece grindingto determine whether the corrections made from earlier measurementssufficiently compensate for any unwanted process induced eccentricity,and further corrections may be made to the wheelfeed programinstructions or control signals as required. The process may be repeateduntil the measurements made on a test workpiece indicate that theunwanted eccentricity of each ground region is within desired limits.Thereafter the grinding machine wheelfeed may be controlled to grindfurther workpieces in accordance with the finally modified wheelfeedprogram instructions or control signals.

(d) Multiple Workpiece Measuring For Setting Up

Instead of producing only one workpiece on which measurements are madeduring setting up, it may be preferable at each stage to grind a numberof workpieces which together form a sample, and to perform eccentricitymeasurements on the workpieces in each sample, and thereby determine theextent of any unwanted eccentricity both in terms of angular positionand radial extent for each region of each workpiece in each sample, andto determine the mean unwanted eccentricity and mean angular position ofsuch eccentricity for each sample, for use as the basis for thecorrection to the wheel feed control signals for subsequent grinding.

Where plural samples of workpieces are used to determine the correctionsto be made, the process for determining what is to be the final set ofcontrol signals for the wheelfeel, can be terminated either if all ofthe measurements of unwanted eccentricity in all of the workpieces in asample fall within desired limits, or if the mean of all themeasurements of unwanted eccentricity fall within desired limits. Theparticular criterion used may depend upon the specification for thecomponent concerned.

(e) Operational Modes of Machine Control System

According to a preferred feature of the invention, the control systemfor controlling the wheel feed may operate in different modes.

A first mode allows rapid advances and retraction of the grinding wheel,and rapid relative lateral movement of the wheel and the workpiece, tofacilitate workpiece mounting and demounting and relative axialpositioning of the wheel and the workpiece.

A second mode is provided for when the grinding wheel is grinding aconcentric cylindrical region of a workpiece. Here small unwantedeccentricity can be introduced by grinding process forces, the unwantedeccentricity can be compensated by introducing small complementaryforward and backward movement of the grinding wheel in step with therotation of the workpiece so as actually to grind the cylindrical regioneccentrically relative to the primary workpiece axis, but by an amountjust sufficient to cancel out the process induced eccentricity.

In a third mode the grinding wheel can be advanced and retracted throughconsiderable distances in step with the rotation of the eccentric regionof the workpiece as the latter is rotated, so as to follow the muchgreater eccentricity of an eccentric cylindrical workpiece surface (suchas the crankpin of a crankshaft).

If correction of process induced eccentricity in the eccentriccylindrical surfaces is also required, a further mode is added to theknown mode, in which the wheel feed control causes the wheel to followthe excessive eccentric rotation of an eccentric workpiece region, inwhich the eccentric following movement is corrected by smaller backwardand forward shifts of the wheel correctly in step with the workpiecerotation so as to compensate for any unwanted process inducedeccentricity introduced into the eccentric cylindrical surface by thegrinding process.

(f) Grinding Methods Employing the Invention

The invention also lies in a method of grinding concentric and eccentricregions of similar composite workpieces by a computer controlledgrinding machine comprising the steps of setting up modified wheelfeedprogram instructions or control signals by any of the aforesaid methods,and thereafter when grinding cylindrical surfaces of compositeworkpieces similar to that used in the setting up process, using themodified wheel feed program instructions or control signals derived fromthe setting up procedure, to control the wheelfeed drive.

By using a high speed CBN grinding wheel, it is possible to eliminatethe rough machining step typically required before a fine grinding stepto produce a bearing surface, thereby allowing a two stage grinding andpolishing process to produce a finished product, instead of a threestage process.

The invention thus allows the known software controlled crankpinfollowing facility incorporated computer controlled grinding machines topermit a grinding wheel to follow the relative eccessive eccentricmovement of a crankpin during grinding as the crankshaft rotates, to beutilised, albeit acting at a smaller scale, to compensate for unwantedeccentricity introduced into cylindrically ground surfaces of aworkpiece which should be concentric as a consequence of grindingprocess forces exerted, as such surfaces are ground and which tend toappear when the workpiece is stress relieved.

This aspect of the invention thus in effect provides for grinding ofeccentric cylindrical surfaces of a workpiece in known manner, andeccentrically grinding cylindrical surfaces of the same workpieces whichare to be concentric about the primary workpiece axis the degree ofeccentricity being such that when a ground workpiece is stress relievedafter grinding, the region in fact will be concentric relative to theprimary axis of the workpiece.

Whilst the invention is of particular application to the grinding ofcrankpins and journal bearing regions on elongate crankshafts, it is tobe understood that it is equally applicable to the grinding of anycomposite workpiece so as to remove eccentricity which the grindingprocess can introduce into the workpiece, and which becomes evident asthe latter becomes unstressed.

(g) Grinding Machine

A computer controlled grinding machine for performing methods ofgrinding as aforesaid comprises a grinding wheel, drive means forrotating the wheel, wheelfeed drive means for advancing and withdrawingthe grinding wheel towards and away from a workpiece region in a precisemanner, computer means for controlling the wheelfeed drive means, whichcomputer means includes memory means for storing programmable wheel feedinstructions whereby the position of the wheel at each instant during agrinding process can be controlled, and program means loaded into thecomputer to control the wheel feed drive and the position of thegrinding wheel so as to control, at selected region along the workpiece,the advance and withdrawal of the grinding wheel before during and aftergrinding each said region, so that eccentric and concentric cylindricalgrinding of different workpiece regions may be performed withoutdemounting the workpiece.

Where the grinding machine introduces unwanted eccentricity intoconcentrically ground cylindrical workpiece surfaces, the computer meansmay include memory means for storing correcting or corrected wheelfeedprogram instructions or control signals for use during the grinding ofsuch regions, which correcting or corrected instructions or signals areobtained from any one of the setting up processes described above.

PRODUCTS PRODUCED BY THE PROCESS

The invention also lies in workpieces when made in accordance with anyof the aforesaid methods or using the aforesaid grinding machine.

The invention will now be described by way of example with reference tothe accompanying drawings, in which:

FIG. 1 illustrates a computer controlled grinding machine, fitted withan in process gauge;

FIG. 2 is a side view of the gauge to an enlarged scale;

FIG. 3 is a diagrammatic illustration of how a gauge is controlled andin turn controls the grinding cycle, via the machine controllingcomputer; and

FIG. 4 an example of the grinding process steps of one method accordingto the invention.

DETAILED DESCRIPTION OF THE DRAWING

FIG. 1 shows a grinding machine 10 having a grinding wheel 12 driven bya motor 14 and mounted on a wheelhead 16 for movement towards and awayfrom a workpiece 18 along a linear track 20 under the control of thewheelfeed drive motor 22. The workpiece 18 is mounted on a carriage 70itself slidable on a slideway 72 and driven therealong to position theworkpiece relative to the wheel, via a drive 74. The workpiece ismounted between centers in a tailstock 24 and a headstock 26 (themselvesmounted on the carriage 70). The headstock houses a motor (not shown)for rotating the workpiece 18 via a chuck 28. The workpiece shown is acrankshaft of an internal combustion engine and includes offsetcrankpins 30 (which are eccentric to the main workshaft axis), andcylindrical bearing regions 31, which are to be ground to size, eachbearing region constituting a cylindrical workpiece region for grindingwhich should be concentric with the workpiece axis.

A computer 32 loaded with workpiece data and operating programs (such asare to be described) controls the operation of the machine and interalia moves the wheelhead 16 towards and away from the workpiece 18 asthe workpiece rotates, so as to maintain contact between the wheel andthe journal bearing region being ground. Some data can be entered viathe keyboard 33. Data/results/process steps can be displayed on thescreen 35.

A gauge, generally designated 34, is carried by the wheel head assemblyfor gauging the diameter of the regions being ground. This can be donewhile the workpiece is rotated slowly, and preferably without thegrinding wheel in contact, after grinding. The gauge is shown in itsparked, non-operating position in FIG. 1. During gauging it is advancedso that the fingers of the gauge (described in more detail withreference to FIG. 2) are first located on the opposite side of theworkpiece from the wheel 12, so that they can be lowered and moved backtowards the wheel so as to be located above and below the workpiece, andthen moved towards the latter until they touch it at diametricallyopposite regions for gauging.

The gauge will allow the gauging of crankpins such as 30 as they areground, but FIG. 2 shows how the fingers 36 and 38 can also engage acylindrical bearing region 31. Pneumatic drives 44, 46 and 48 producerelative movement between the gauge assembly and the wheelhead 16,between the gauge assembly and the workpiece, and between the twofingers 36 and 38.

A sensor 50 determines the spacing between the fingers 36, 38 andprovides a size signal for the computer 32, from which the diameter ofthe workpiece region between the fingers can be computed. The sensor canalso provide a signal indicative of the linear oscillatory movement ofthe gauge fingers caused by any eccentricity in the ground region, bylocking the two fingers 36, 38 together but spaced so as to just lightlyclamp the workpiece therebetween, and rotating the latter slowly andobserving any movement of 38 relative to sensor 50.

FIG. 3 shows diagrammatically the grinding wheel 12, the wheelhead 16,the slide 20, and a different type of gauge from that shown in FIGS. 1and 2. This engages a cylindrical bearing region 31 by means of twofixed converging fingers 52, 54, with a sensor 55 producing a signalfrom which the distance between the converging fingers at which thefingers make contact with the workpiece can be determined. The computer32 receives the signal along line 56 and can compute therefrom thediameter of the workpiece region. Position and wheelhead drive signalsfrom the computer 32 pass via line 59. Not shown are the signal pathsfrom the computer 32 to the other drives for moving the gauge into andout of engagement and controlling the speed of rotation of the wheel andthe crankshaft. Although developed to measure crankpin during grinding,this type of gauge can also be used to determine any eccentricity in therotating workpiece region, by urging the gauge fingers 52, 54 intocontact as shown and converting any in line movement of the gaugeassembly 60, due to eccentricity, as the workpiece rotates into anappropriate electrical signal using a transducer such as 57.

Wheel position signals from a transducer/encoder 41 are passed to thecomputer 32 via line 43.

An encoder 37 or other transducer converts rotation of the cylindricalbearing region 31 of the workpiece 18 into angular informature. Signalsalong line 39 enable the phase of any eccentricity of 31 to bedetermined by the computer 32.

As described in our copending UK Application 9702550.6 which describes amethod of guiding crankpins to size using in process gauging, atechnique is also described to obtain a high quality surface finish andhighly accurate diameters of ground components. This technique may alsobe used when grinding journal bearing regions. Thus during grinding, aninitial fast wheelfeed may be used to roundout cylindrical bearingregion 31, and the fast grinding feed stopped after a fixed feed amountindependent of the gauge. At the end of the fast feed the gauge 34 isused by the machine control computer to sample the size of the region 31and to check any eccentricity in magnitude and angular position asdetermined by the rotated position of the workpiece at which theeccentricity is noted. A prerequisite for the grinding cycle to proceedbeyond this point is that this sample of size sensibly confirms that thegauge is on the region and functioning properly.

After computing the necessary control signal to compensate for anymeasured eccentricity the grinding feed restarts. A lower feed rate maybe used.

In normal operation the feed will be stopped in response to signalsderived from the wheel position and/or the in-process gauge 34 in adiameter measuring mode, and sampled by the machine control computer 32.

In a method, which involves in process gauging as the grinding feedproceeds towards a target size, near final size the instantaneous sizeof the region 31 being ground can be continuously sampled by the machinecontrol computer.

If one or two or more consecutive samples of region 31 size, are foundto be at or below the target size, the controlling computer immediatelystops the grinding feed and initiates a feed dwell. This dwell, measuredas N workpiece turns, permits the region being ground to achieve goodgeometric roundness and a stable size. This procedure gives an optimumresponse to fast grinding feeds commensurate with fast manufacturingtimes. During this feed dwell, typically two work revolutions, thecontrolling computer stores a number of consecutive samples of sizemeasured at different angular positions relative to the gauge fingers sothat it can calculate an average value of the workpiece region diameter.

At the completion of this dwell, the average diameter value may becalculated, and this value used to calculate the feed distance toachieve the desired final size of the region. The controlling computerthen initiates an incremental feed to final size. At the start of thisincremental feed, the gauge, having completed its work, can beretracted, with the object of minimising manufacturing time. Because thefeed to final size is not being controlled by gauge, it does not have tobe slow but can be optimized to to eliminate the build-up of machiningvibrations and/or minimize machining time.

After a final “sparkout feed dwell”, measured as n workpiece turns, thegrinding wheel can be retracted, initially at a slow rate so as not toleave any grinding wheel breakaway mark, and then at a faster rate tominimize manufacturing time.

Alternatively, machining may be achieved without such in processgauging, simply by controlling the wheel feed and gauging componentsoff-line, and correcting for process induced eccentricity in accordancewith the present invention and for wheel wear by appropriate adjustmentas the grinding of a batch of workpieces progresses.

FIG. 4 illustrates the steps of a method of grinding an elongatecomponent having a number of different regions therealong which are tobe cylindrically ground either concentrically or eccentrically to theprimary axis of the component, and in which process induced eccentricityis corrected for all such regions whether ground to be concentric oreccentric to the primary axis.

Detailed program steps required to set up and operate a grinding machinein different ways in accordance with different aspects of the invention,so as to allow so-called composite workpieces to be ground on the samecomputer controlled grinding machine, with or without correction forprocess induced eccentricity, are now listed, on the following pages.

The lists of controlled operations which follow illustrate the stepswhich the machine controlling computer must initiate the inputs it mustrespond to, and the decisions it must make, under the control ofprograms loaded into its memory, so as to adjust the wheelfeed programinstructions or control signals and other machine parameters, and parts,so as to set up the machine to therafter grind a composite workpiecesuch as a crankshaft in accordance with different methods embodying theinvention, as detailed.

A brief explanation of the process to which the steps relate is providedat the head of each listing.

I. Instructions for setting up and running a computer controlledgrinding machine to grind similar composite workpieces withouteccentricity correction of cylindrically ground regions of the workpiece

1. Load composite workpiece data into machine computer

2. Load wheelfeed routines into machine computer

3. Identify axial positions of workpiece regions to be ground

4. Mount workpiece

5. Rotate workpiece for grinding

6. Align grinding wheel with region to be ground

7. Determine from workpiece data how region is to be ground

8. If concentric grinding, go to 9; if eccentric go to 28

9. Select concentric wheelfeed grinding routine

10. Advance wheel to engage workpiece region

11. Compute wheel position to achieve a target diameter

12. Grind and measure wheel advance from engagement

13. Stop wheelfeed at target diameter position

14. Disengage wheel

15. Apply gauge and measure ground diameter

16. Adjust wheelfeed instructions to achieve final diameter

17. Compute wheel position to achieve final diameter

18. Advance wheel to engage workpiece

19. Grind and measure wheel advance from engagement

20. Stop wheelfeed when computed position is achieved

21. Retract wheel

22. More regions to grind? Yes or No

23. If Yes, go to 6; if No go to 24

24. Demount workpiece

25. More workpieces? Yes or No

26. If Yes, go to 4; if No, go to 27

27. Enter standby mode

28. Select eccentric wheelfeed grinding routine

29. Go to 10

II. Instructions for setting up and grinding a computer controlledgrinding machine to grind similar composite workpieces with eccentricitycorrection of cylindrically ground concentric regions thereof

1. Load composite workpiece data into machine computer

2. Load wheelfeed routines into machine computer

3. Identify axial positions of workpiece regions to be ground

4. Mount workpiece

5. Rotate workpiece for grinding

6. Align grinding wheel with region to be ground

7. Determine from workpiece data how region is to be ground

8. If concentric grinding, go to 9; if eccentric go to 31

9. Select concentric grinding wheelfeed routine

10. Advance wheel to engage workpiece region

11. Compute wheel position to achieve a target diameter

12. Grind and measure wheel advance from engagement

13. Stop wheelfeed at target diameter position

14. Disengage wheel

15. Rotate workpiece slowly

16. Gauge ground region and store diameter

17. Identify any eccentricity and its rotational position

18. Adjust selected wheelfeed routine for eccentricity

19. Compute wheel position to achieve final diameter

20. Rotate workpiece for grinding

21. Advance wheel and engage workpiece region

22. Regrind using adjusted routine and measure wheel advance

23. Stop wheelfeed when computed position is achieved

24. Retract wheel

25. More regions to grind? Yes or No

26. If Yes, go to 6; if No, go to 27

27. Demount workpiece

28. More workpieces? Yes or No

29. If Yes go to 4; if No go to 30

30. Enter standby mode

31. Select eccentric grinding wheelfeed routine

32. Advance wheel to enage workpiece region

33. Compute wheel position to achieve target diameter

34. Grind and measure wheel advance and engagement

35. Stop wheelfeed at computed position

36. Disengage wheel from eccentric workpiece region

37. Apply gauge and measure diameter of eccentric region

38. Adjust wheelfeed to achieve final diameter

39. Compute wheel position to achieve final diameter

40. Advance wheel to engage eccentric workpiece region

41. Grind and measure wheel advance from engagement

42. Stop wheelfeed when computed position is achieved

43. Retract wheel and go to 25

What is claimed is:
 1. A method of grinding a composite workpiece toform a component having concentric and eccentric cylindrical regions,comprising, mounting the workpiece for rotation about a primary axis ina computer controlled grinding machine, the grinding machine having agrinding wheel the advance and withdrawal of which is controllable by aprogram entered into the machine controlling computer, loading wheelfeedcontrolling program into the computer, positioning the grinding wheelrelative to the workpiece, or the workpiece relative to the grindingwheel, so that the wheel is aligned with a first selected region of theworkpiece, advancing the grinding wheel towards the selected region soas to grind the surface thereof, controlling a wheelfeed so as tomaintain grinding contact between the grinding wheel and the workpieceso as either to grind a concentric cylindrical region thereon or aneccentric offset cylindrical region thereon as required, informationabout each selected region of the workpiece being stored in the computerand addressed as appropriate so that the wheelfeed can be controlledappropriately depending on whether a selected workpiece region is to beground as a concentric or an eccentric offset cylindrical region, inwhich the wheelfeed controlling program is programmed so as to be ableto distinguish between concentric and eccentric regions of a workpiecefrom workpiece data stored therein to enable the wheelfeed to becontrolled accordingly so as to grind as required a cylindrical surfaceconcentric with a primary axis of the workpiece or a cylindrical surfacewhich is eccentric thereto, whose axis is spaced from but parallel tothe said primary axis, and which is also programmed to introduce smalladvance and retract movements in the wheelfeed while the grinding wheelis engaged in grinding a concentric cylindrical workpiece region so asto introduce into the ground region an opposing eccentricity in thecylindrical surface which is equal and opposite to any eccentricitywhich grinding process forces introduce into the ground region, so thatthe two eccentricities cancel out.
 2. The method of claim 1, when usedto grind a crankshaft which has journal bearing regions which have to beground as cylindrical surfaces concentric with the primary crankshaftaxis and crankpins which have to be ground as cylindrical surfacesoffset from and eccentric to the primary crankshaft axis.
 3. A method ofgrinding a workpiece having both concentric and eccentric offsetcylindrical regions thereon using a single grinding machine undercomputer control without demounting the workpiece from the machine, inwhich the computer is loaded with data about the workpiece, howdifferent regions are to be ground, and wheelfeed instructions, and thegrinding process is adjusted for each region as detailed by theworkpiece and region data stored in the computer, thereby enabling aworkpiece to be left in place between centers while different regionstherealong are ground to form cylindrical surfaces some of which areconcentric with a primary axis of rotation of the workpiece and othersof which are eccentric offset thereto, in which control is programmed soas to be able to distinguish between concentric and eccentric regions ofa workpiece from workpiece data stored therein to enable a wheelfeed tobe controlled accordingly so as to grind as required a cylindricalsurface concentric with a primary axis of the workpiece or a cylindricalsurface which is eccentric thereto, whose axis is spaced from butparallel to the said primary axis, and which is also programmed tointroduce small advance and retract movements in the wheelfeed while agrinding wheel is engaged in grinding a concentric cylindrical workpieceregion so as to introduce into the ground region an opposingeccentricity in the cylindrical surface which is equal and opposite toany eccentricity which grinding process forces introduce into the groundregion, so that the two eccentricities cancel out.
 4. A computercontrolled grinding machine for grinding a composite workpiececomprising a grinding wheel, drive means for rotating the wheel,wheelfeed drive means for advancing and withdrawing the grinding wheeltowards and away from a workpiece region in a precise manner, computermeans for controlling the wheelfeed drive means, which computer meansincludes memory means for storing programmable wheelfeed instructionswhereby the position of the wheel at each instant during a grindingprocess can be controlled, program means loaded into the computer tocontrol the wheelfeed drive and the position of the grinding wheel, orthe workpiece, so as to control, at selected regions along theworkpiece, the advance and withdrawal of the grinding wheel beforeduring and after grinding each said region, so that eccentric andconcentric cylindrical grinding of different workpiece regions may beperformed without demounting the workpiece, wherein the grinding processintroduces unwanted eccentricity into concentrically ground cylindricalworkpiece surfaces of the composite workpiece, and the computer meansincludes memory means for storing corrected wheelfeed programinstructions or signals for use during the grinding of such regions. 5.A computer controlled grinding machine according to claim 4, the machinebeing adapted to modify basic wheelfeed commands which unmodified willcontrol the wheelfeed to grind an eccentric cylindrical surface, so asto introduce an additional eccentricity which is equal and opposite toany stress-induced eccentricity introduced into the eccentriccylindrical surface by the grinding process.
 6. A method of setting up acomputer controlled grinding machine for grinding concentric andeccentric cylindrical regions of an elongate composite workpiece, theworkpiece being supported at its opposite ends for grinding thereof, inwhich axial variations in unwanted eccentricity introduced by thegrinding process are taken into account, such that regions towards thecenter of the workpiece tend to require a greater degree of eccentricitycompensation than do those adjacent said opposite ends, said methodcomprising the steps of advancing a grinding wheel towards a selectedregion so as to selectively grind either a concentric or an eccentriccylindrical region thereon as required, cylindrically grinding all ofsaid concentric cylindrical regions of the workpiece without introducingany compensation for unwanted process-induced eccentricity, thereaftermaking measurements on the workpiece to determine the extent and angularposition of any unwanted eccentricity for each of the ground regions,and separately adjusting wheelfeed program instructions or controlsignals to be used to control wheelfeed during subsequent grinding ofeach said concentric or eccentric region of the same or similarworkpieces, so as to compensate individually for each said region forany process-induced eccentricity.
 7. A method as claimed in claim 6,wherein after the setting up process has been performed the originalworkpiece is reground using the wheelfeed instructions or controlsignals, and a further gauging is performed on the reground workpieceand second order corrections are made to the program instructions orcontrol signals, before regrinding the original workpiece or grindingfurther similar workpieces.
 8. A method of grinding cylindrical surfacesof a crankshaft having concentric and eccentric cylindrical regionswhich uses a software controlled crankpin following facilityincorporated into a computer controlled grinding machine to permit agrinding wheel to follow the relatively excessive eccentric movement ofthe crankpins of the crankshaft during the grinding of the crankshaft asthe crankshaft rotates, and which at a smaller scale introduces acomplementary eccentricity for removing unwanted eccentricity introducedinto the concentric cylindrically ground surfaces of the crankshaft as aconsequence of grinding process forces exerted as such surfaces areground, and which tends to appear after the crankshaft is stressrelieved, so as to cancel out the grinding process induced eccentricity.9. A method of operating a computer controlled grinding machine to grinda composite workpiece, using a grinding wheel so as to eccentricallygrind a region of the workpiece which is to have a concentriccylindrical surface relative to the workpiece primary axis aftergrinding, rather than concentrically grinding the said region, thedegree of eccentricity being such that when the ground workpiece isstress relieved after grinding, the region will be concentric relativeto the primary axis of the workpiece, and wherein a similar computercontrol of wheelfeed albeit at a larger scale is employed to alloweccentric offset cylindrical surfaces of the workpiece also to beground, using said wheel on the grinding machine.
 10. Compositeworkpieces when made in accordance with the method of grinding acomposite workpiece to form a component having concentric and eccentriccylindrical regions, comprising, mounting the workpiece for rotationabout a primary axis in a computer controlled grinding machine, thegrinding machine having a grinding wheel the advance and withdrawal ofwhich is controllable by a program entered into the machine controllingcomputer, loading a wheelfeed controlling program into the computer,positioning the grinding wheel relative to the workpiece, or theworkpiece relative to the grinding wheel, so that the wheel is alignedwith a first selected region of the workpiece, advancing the grindingwheel towards the selected region so as to grind the surface thereof,controlling a wheelfeed so as to maintain grinding contact between thegrinding wheel and the workpiece so as either to grind a concentriccylindrical region thereon or an eccentric offset cylindrical regionthereon as required, information about each selected region of theworkpiece being stored in the computer and addressed as appropriate sothat the wheelfeed can be controlled appropriately depending on whethera selected workpiece region is to be ground as a concentric or aneccentric offset cylindrical region, in which the wheelfeed controllingprogram is programmed so as to be able to distinguish between concentricand eccentric regions of a workpiece from workpiece data stored thereinto enable the wheelfeed to be controlled accordingly so as to grind asrequired a cylindrical surface concentric with a primary axis of theworkpiece or a cylindrical surface which is eccentric thereto, whoseaxis is spaced from but parallel to the said primary axis, and which isalso programmed to introduce small advance and retract movements in thewheelfeed while the grinding wheel is engaged in grinding a concentriccylindrical workpiece region so as to introduce into the ground regionan opposing eccentricity in the cylindrical surface which is equal andopposite to any eccentricity which grinding process forces introduceinto the ground region, so that the two eccentricities cancel out.
 11. Acomputer program for setting up a computer controlled grinding machineto set up wheelfeed instructions to control the grinding of compositeworkpieces comprising the following steps:
 1. Load composite workpiecedata into machine computer
 2. Load wheelfeed routines into machinecomputer
 3. Identify axial positions of workpiece regions to be ground4. Mount workpiece
 5. Rotate workpiece for grinding
 6. Align grindingwheel with region to be ground
 7. Determine from workpiece data howregion is to be ground
 8. If concentric grinding, go to 9; if eccentricgo to 28
 9. Select concentric wheelfeed grinding routine
 10. Advancewheel to engage workpiece region
 11. Compute wheel position to achieve atarget diameter
 12. Grind and measure wheel advance from engagement 13.Stop wheelfeed at target diameter position
 14. Disengage wheel
 15. Applygauge and measure ground diameter
 16. Adjust wheelfeed instructions toachieve final diameter
 17. Compute wheel position to achieve finaldiameter
 18. Advance wheel to engage workpiece
 19. Grind and measurewheel advance from engagement
 20. Stop wheelfeed when computed positionis achieved
 21. Retract wheel
 22. More regions to grind? Yes or No 23.If Yes, go to 6; if No go to 24
 24. Demount workpiece
 25. Moreworkpieces? Yes or No
 26. If Yes, go to 4; if No, go to 27
 27. Enterstandby mode
 28. Select eccentric wheelfeed grinding routine
 29. Go to10.
 12. A computer program for setting up and operating a computercontrolled grinding machine to grind similar composite workpieces witheccentricity correction of concentrically ground regions, comprising thesteps of:
 1. Load composite workpiece data into machine computer
 2. Loadwheelfeed routines into machine computer
 3. Identify axial positions ofworkpiece regions to be ground
 4. Mount workpiece
 5. Rotate workpiecefor grinding
 6. Align grinding wheel with region to be ground 7.Determine from workpiece data how region is to be ground
 8. Ifconcentric grinding, go to 9; if eccentric go to 31
 9. Select concentricgrinding wheelfeed routine
 10. Advance wheel to engage workpiece region11. Compute wheel position to achieve a target diameter
 12. Grind andmeasure wheel advance from engagement
 13. Stop wheelfeed at targetdiameter position
 14. Disengage wheel
 15. Rotate workpiece slowly 16.Gauge ground region and store diameter
 17. Identify any eccentricity andits rotational position
 18. Adjust selected wheelfeed routine foreccentricity
 19. Compute wheel position to achieve final diameter 20.Rotate workpiece for grinding
 21. Advance wheel and engage workpieceregion
 22. Regrind using adjusted routine and measure wheel advance 23.Stop wheelfeed when computed position is achieved
 24. Retract wheel 25.More regions to grind? Yes or No
 26. If Yes, go to 6; if No, go to
 2727. Demount workpiece
 28. More workpieces? Yes or No
 29. If Yes go to 4;if No go to 30
 30. Enter standby mode
 31. Select eccentric grindingwheelfeed routine
 32. Advance wheel to enage workpiece region 33.Compute wheel position to achieve target diameter
 34. Grind and measurewheel advance and engagement
 35. Stop wheelfeed at computed position 36.Disengage wheel from eccentric workpiece region
 37. Apply gauge andmeasure diameter of eccentric region
 38. Adjust wheelfeed to achievefinal diameter
 39. Compute wheel position to achieve final diameter 40.Advance wheel to engage eccentric workpiece region
 41. Grind and measurewheel advance from engagement
 42. Stop wheelfeed when computed positionis achieved
 43. Retract wheel and go to 25.